Image forming apparatus with accurate temperature control for various media having different thickness

Abstract

Disclosed is a fixing apparatus, in which a cylindrical roller comprising a thin metal layer having a small heat capacity is heated by an induction heating and, when the toner image transferred onto a paper sheet is fixed to the paper sheet, it is possible to control accurately the temperature on the surface of the cylindrical roller. Where the toner image formation on the paper sheet having a width smaller than the length of the cylindrical roller and the fixing operation of the toner image are carried out repeatedly, it is possible to prevent the temperature elevation in the edge portion of the roller. In addition, the power consumption can be saved.

What is claimed is:  
     
       1. A fixing apparatus, comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to apply a predetermined pressure to said endless member;  
       an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member;  
       a temperature detecting apparatus for detecting the temperature of the endless member, said temperature detecting apparatus being arranged at a point of about 90° along the outer circumferential surface of the endless member from the pressurizing point at which said pressurizing member applies pressure to the endless member; and  
       an abnormal temperature detecting apparatus for detecting the temperature of said endless member, said abnormal temperature detecting apparatus being arranged at a point of about 90° along the outer circumferential surface of the endless member from the pressurizing point at which said pressurizing member applies pressure to the endless member.  
     
     
       2. The fixing apparatus according to  claim 1 , wherein said abnormal temperature detecting apparatus is positioned upstream of said pressurizing point at which said pressurizing member applies pressure to the endless member. 
     
     
       3. A fixing apparatus, comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to apply a predetermined pressure to said endless member;  
       an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member, said induction heating apparatus comprising a planar coil wound in the circumferential direction of said endless member; and  
       an abnormal temperature detecting apparatus for detecting the temperature of the endless member, said temperature detecting apparatus being arranged at a point of about 90° along the outer circumferential surface of the endless member from the pressurizing point at which said pressurizing member applies pressure to the endless member,  
       wherein said temperature detecting apparatus is positioned at a point where the endless member generates the largest amount of heat when the endless member, which is stopped, is heated by said induction heating apparatus.  
     
     
       4. The fixing apparatus according to  claim 3 , wherein said abnormal temperature detecting-apparatus detects the abnormality of the surface temperature of said endless member in a plane substantially parallel to the direction in which said endless member is pushed by said pressurizing member. 
     
     
       5. A fixing apparatus, comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to apply a predetermined pressure to said endless member;  
       an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member;  
       a first temperature detecting apparatus arranged in that position on the surface of the endless member through which passes the minimum size of a transferred material so as to detect the temperature of the endless member;  
       a second temperature detecting apparatus arranged outside that region on the surface of the endless member through which passes the maximum size of a transferred material so as to detect the temperature of the endless member; and  
       cooling means having at least one of a fan and a fan provided with a filter for cooling the edge portion of the endless member in accordance with the difference between the temperatures detected by said first temperature detecting apparatus and said second temperature detecting apparatus, wherein:  
       when the difference between the temperatures detected by said first and second temperature detecting apparatuses exceeds a predetermined value, power supplied to said induction heating apparatus is gradually reduced until the first temperature detecting apparatus detects a lowest possible fixing temperature; and  
       when said first temperature detecting apparatus detects the lowest possible fixing temperature, and the difference between the temperatures detected by said first and second temperature detecting apparatuses still exceeds the predetermined value, said cooling means is operated during a predetermined time period.  
     
     
       6. The fixing apparatus according to  claim 5 , wherein said cooling means gradually lowers the temperature control value detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus and after the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus has reached a predetermined temperature, serves to cool the edge portion of said endless member. 
     
     
       7. A fixing apparatus comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to apply a predetermined pressure to said endless member;  
       an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member;  
       a first temperature detecting apparatus arranged in that position on the surface of the endless member through which passes the minimum size of a transferred material so as to detect the temperature of the endless member;  
       a second temperature detecting apparatus arranged outside that region on the surface of the endless member through which passes the maximum size of a transferred material so as to detect the temperature of the endless member; and  
       cooling means for cooling the edge portion of the endless member in accordance with the difference in temperatures detected by said first temperature detecting apparatus and said second temperature detecting apparatus,  
       wherein said cooling means is rotated at a first speed when a transferred material is transferred to a nip portion between said endless member and said pressurizing member, and is rotated at a second speed lower than said first speed when a transferred material is not transferred to said nip portion between said endless member and said pressurizing member.  
     
     
       8. The fixing apparatus according to  claim 7 , wherein said cooling means gradually lowers the temperature detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus, is rotated in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus at any of the timing when the temperature detected by said first temperature detecting apparatus is gradually lowered to permit said first temperature detecting apparatus to detect the critical temperature at which the fixation can be performed, and when the difference between the temperature detected by the first temperature detecting apparatus and the temperature detected by the second temperature detecting apparatus has reached a predetermined temperature. 
     
     
       9. A fixing apparatus comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to applying a predetermined pressure to said endless member;  
       an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member;  
       a first temperature detecting apparatus arranged in that position on the surface of the endless member through which passes the minimum size of a transferred material so as to detect the temperature of the endless member;  
       a second temperature detecting apparatus arranged outside that region on the surface of the endless member through which passes the maximum size of a transferred material so as to detect the temperature of the endless member; and  
       cooling means, having at least one of a fan and a fan provided with a filter, for cooling the edge portion of the endless member in accordance with the difference between the temperatures detected by said first temperature detecting apparatus and said second temperature detecting apparatus,  
       wherein:  
       when the difference between the temperatures detected by said first and second temperature detecting apparatuses exceeds a predetermined value, power supplied to said induction heating apparatus is gradually reduced until the first temperature detecting apparatus detects a lowest possible fixing temperature; and  
       when said first temperature detecting apparatus detects the lowest possible fixing temperature, and the difference between the temperatures detected by said first and second temperature detecting apparatuses still exceeds the predetermined value, said cooling means is operated during a predetermined time period on the basis of the difference between the temperatures detected by said first and second temperature detecting apparatuses.  
     
     
       10. The fixing apparatus according to  claim 9 , wherein said cooling means includes a fan and an ozone filter. 
     
     
       11. The fixing apparatus according to  claim 10 , wherein said cooling means gradually lowers the temperature detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first detecting apparatus, serves to cool the edge portion of said endless member in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus. 
     
     
       12. An image forming apparatus, comprising: 
       a photosensitive body holding a latent image;  
       a developing apparatus for supplying a developing agent onto said latent image formed on said photosensitive body so as to visualize said latent image;  
       a transfer apparatus for transferring the developing agent image formed on said photosensitive body by said developing apparatus onto a transferred material;  
       a fixing apparatus including (i) an endless member having a metal layer made of a conductor and rotatable in an optional direction, (ii) a pressurizing member serving to apply a predetermined pressure to said endless member, (iii) an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member, (iv) a first temperature detecting apparatus arranged in that position on the surface of the endless member through which passes the minimum size of a transferred material so as to detect the temperature of the endless member, and (v) a second temperature detecting apparatus arranged outside that region on the surface of the endless member through which passes the maximum size of a transferred material so as to detect the temperature of the endless member;  
       control means for controlling power supplied to the induction heating apparatus of said fixing apparatus; and  
       cooling means, having at least one of a fan and a fan provided with a filter, for cooling the edge portion of the endless member in accordance with the difference between the temperatures detected by the first temperature detecting apparatus and the second temperature detecting apparatus,  
       wherein:  
       when the difference between the temperatures detected by the first and second temperature detecting apparatuses exceeds a predetermined value, said control means controls the power supplied to the induction heating apparatus to gradually reduce the power, until the first temperature detecting apparatus detects a lowest possible fixing temperature; and  
       when the first temperature detecting apparatus detects the lowest possible fixing temperature, and the difference between the temperatures detected by the first and second temperature detecting apparatuses still exceeds the predetermined value, said cooling means is operated during a predetermined time period.  
     
     
       13. The fixing apparatus according to  claim 12 , wherein said cooling means gradually lowers the temperature detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus and after the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus has reached a predetermined temperature, serves to cool the edge portion of said endless member. 
     
     
       14. The fixing apparatus according to  claim 13 , wherein said cooling means is rotated at a first speed when a transferred material is transferred to a nip portion between said endless member and said pressurizing member, and is rotated at a second speed lower than said first speed when a transferred material is not transferred to said nip portion between said endless member and said pressurizing member. 
     
     
       15. The fixing apparatus according to  claim 12 , wherein said cooling means gradually lowers the temperature detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus, is rotated in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus at any of the timing when the temperature detected by said first temperature detecting apparatus is gradually lowered to permit said first temperature detecting apparatus to detect the critical temperature at which the fixation can be performed, and when the difference between the temperature detected by the first temperature detecting apparatus and the temperature detected by the second temperature detecting apparatus has reached a predetermined temperature. 
     
     
       16. An image forming apparatus comprising: 
       a photosensitive body holding a latent image;  
       a developing apparatus for supplying a developing agent onto said latent image formed on said photosensitive body so as to visualize said latent image;  
       a transfer apparatus for transferring the developing agent image formed on said photosensitive body by said developing apparatus onto a transferred material;  
       a fixing apparatus having an endless member including a metal layer formed of a conductor and rotatable in an optical direction, a pressurizing member for applying a predetermined pressure to said endless member, and a heating device arranged in the vicinity of the endless member for heating the endless member, the transferred material having said developing agent image transferred thereto by said transfer apparatus and the developing agent image itself being heated and pressurized so as to fix the developing agent image onto the transferred material;  
       a cooling apparatus arranged between a first member selected from the endless member and the heating device of the fixing apparatus and a second member selected from the photosensitive body, the developing apparatus and the transfer apparatus, said first member being positioned closest to said second member, for cooling the edge portion of the endless member and apparatus positioned closest to said second member;  
       a first temperature detecting apparatus arranged on the surface of said endless member in a position where the minimum size of the transferred material passes and serving to detect the temperature of the endless member; and  
       a second temperature detecting apparatus arranged on the surface of said endless member outside the region where the maximum size of the transferred material passes and serving to detect the temperature of the endless member;  
       wherein said cooling apparatus is operated in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus.  
     
     
       17. An image forming apparatus comprising: 
       a photosensitive body holding a latent image;  
       a developing apparatus for supplying a developing agent onto said latent image formed on said photosensitive body so as to visualize said latent image;  
       a transfer apparatus for transferring the developing agent image formed on said photosensitive body by said developing apparatus onto a transferred material;  
       a fixing apparatus including (i) an endless member having a metal layer made of a conductor and rotatable in an optional direction, (ii) a pressurizing member serving to apply a predetermined pressure to said endless member, (iii) an induction heating apparatus arranged in the vicinity of said endless member so as to heat the endless member, (iv) a first temperature detecting apparatus arranged in that position on the surface of the endless member through which passes the minimum size of a transferred material so as to detect the temperature of the endless member, and (v) a second temperature detecting apparatus arranged outside that region on the surface of the endless member through which passes the maximum size of a transferred material so as to detect the temperature of the endless member;  
       control means for controlling power supplied to the induction heating apparatus of said fixing apparatus; and  
       cooling means, having at least one of a fan and a fan provided with a filter, for cooling the edge portion of the endless member in accordance with the difference between the temperatures detected by the first temperature detecting apparatus and the second temperature detecting apparatus,  
       wherein:  
       when the difference between the temperatures detected by the first and second temperature detecting apparatuses exceeds a predetermined value, the power supplied to said induction heating apparatus is gradually lowered until the first temperature detecting apparatus detects a lowest possible fixing temperature; and  
       when the first temperature detecting apparatus detects the lowest possible fixing temperature, and the difference between the temperatures detected by said first and second temperature detecting apparatuses still exceeds the predetermined value, said cooling means is operated during a predetermined time period on the basis of the difference between the temperatures detected by the first and second temperature detecting apparatuses.  
     
     
       18. The image forming apparatus according to  claim 17 , wherein said cooling means gradually lowers the temperature detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus, serves to cool the edge portion of said endless member in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus. 
     
     
       19. The fixing apparatus according to  claim 18 , wherein said cooling means is rotated at a first speed when a transferred material is transferred to a nip portion between said endless member and said pressurizing member, and is rotated at a second speed lower than said first speed when a transferred material is not transferred to said nip portion between said endless member and said pressurizing member. 
     
     
       20. The fixing apparatus according to  claim 18 , wherein said cooling means gradually lowers the temperature control value detected by said first temperature detecting apparatus and, after the critical temperature at which the fixation can be performed is detected by said first temperature detecting apparatus, is rotated in accordance with the difference between the temperature detected by said first temperature detecting apparatus and the temperature detected by said second temperature detecting apparatus at any of the timing when the temperature control value detected by said first temperature detecting apparatus is gradually lowered to permit said first temperature detecting apparatus to detect the critical temperature at which the fixation can be performed, and when the difference between the temperature detected by the first temperature detecting apparatus and the temperature detected by the second temperature detecting apparatus has reached a predetermined temperature. 
     
     
       21. A fixing apparatus, comprising: 
       an endless member having a metal layer made of a conductor and rotatable in an optional direction;  
       a pressurizing member serving to apply a predetermined pressure to the endless member;  
       an induction heating apparatus provided in the vicinity of the endless member so as to heat the endless member;  
       a first temperature detecting apparatus provided in that position on the surface of the endless member through which a transferred material of the minimum size passes, so as to detect the temperature of the endless member;  
       a second temperature detecting apparatus provided outside that region on the surface of the endless member through which a transferred material of the maximum size passes, so as to detect the temperature of the endless member; and  
       cooling means having at least one of a fan and a fan provided with a filter for cooling an edge portion of the endless member in accordance with the difference between the temperatures detected by the first temperature detecting apparatus and the second temperature detecting apparatus,  
       wherein when the difference between the temperatures detected by the first and second temperature detecting apparatuses exceeds a predetermined value, the cooling means cools the edge portion of the endless member until the difference is equal to or lower than the predetermined value.  
     
     
       22. A method for controlling a temperature of a fixing apparatus which comprises (i) an endless member extending in a first direction, and rotatable in a second direction perpendicular to the first direction, (ii) a heater member comprising a planar coil formed of wire, a main portion of the planar coil being located parallel to the first direction, the heater member located along an inner periphery of the endless member without contacting the endless member, (iii) a first temperature sensor for detecting a temperature of that portion of the endless member which are other than edge portions there of in the first direction, (iv) a second temperature sensor for detecting a temperature of at least one of the edge portions of endless member, and (v) a cooling member for cooling the endless member, 
       the method comprising the steps of:  
       detecting an output of the first temperature sensor and an output of the second temperature sensor;  
       reducing current to be supplied to a heater member, when the temperature detected by the first temperature falls within a range between an allowable maximum temperature of the endless member and a lower limit temperature of the endless member for a fixing operation; and  
       operating the cooling member until a difference between the temperatures detected by the first and second temperature sensors is lower than a predetermined value. when the difference exceeds the predetermined value.